Leaning Tower illusion: Orientation contrast or perspective distortion? Reply to Maniatis

perspective, as proposed by us (Kingdom et al 2007a, 2007b), but a variant of the Jastrow illusion. Maniatis suggests that the Jastrow illusion is an example of simultaneous size contrast, and that the Leaning Tower illusion is the orientation analog of the Jastrow. In other words the Leaning Tower illusion is an example of simultaneous tilt (or orientation) contrast, or acute-angle expansion, in which acute angles appear greater than they actually are. In fact, this idea was first suggested, and rejected, by Akiyoshi Kitaoka in the news section of his illusion website (http://www.psy.ritsumei.ac.jp/akitaoka/illnews5e.html). Kitaoka's line of reasoning, which we reported in Kingdom et al (2007b), was that the acuteangle expansion explanation would predict a similar-sized illusion in figure 1b, where the arrangement of the inner side of the two child figures is similar to that of the Pisa towers, but in which the figures do not appear to recede. If the illusion was due to acute-angle expansion, one should obtain a similar-sized illusion as with the Pisa towers, whereas if the perspective explanation is correct one should not observe the illusion. The illusion in Kitaoka's figure is tiny or non-existent.